The state Department of Environmental Quality issued a pollution advisory for the Willamette Valley.
The agency suggests that children, older adults and people with heart or lung disease limit their outdoor activities, especially in the evening and early morning when air quality is at its worst.
Wood smoke and diesel exhaust are the main sources of the small pollution particles trapped in the Willamette Valley. Light winds combined with dry, cold air and low nighttime temperatures create inversions that hold the pollution in place.
Controlled fires from two logging operations that crews thought they had extinguished reignited Thursday or Friday, contributing to the smoky pall.
The DEQ asked residents to avoid using wood stoves and fireplaces if at all possible, refrain from outdoor burning, and limit driving and vehicle idling.
The air is likely to remain unhealthy for sensitive people until at least the weekend, and could worsen before then, said Susan Drake, a DEQ air-quality specialist.
Pollution typically gets worse in the evening, when people begin lighting wood stoves for heat, and often lasts into the morning.
The wood smoke creates fine, airborne particles smaller in diameter than a human hair, said Sally Markos, spokeswoman for the Lane Regional Air Protection Authority.
"If you breathe in dust particles, you will cough them out," Markos said. "But fine particles are so small that they go into your lungs and stay there."
In the Eugene-Springfield area, air quality on Saturday declined from good to moderate, where it remained on Sunday. Moderate means that air quality is acceptable, but there may be health concerns for people who are unusually sensitive to air pollution.
In Oakridge, located in a deep valley where many residents use wood stoves for heat, air quality dropped from good to moderate on Friday, then to one step worse &
unhealthy for sensitive groups &
on Saturday. It returned to moderate on Sunday.
Monday's DEQ air advisory was the first since the U.S. Environmental Protection Agency tightened federal standards for the harmful pollution particles known as particulates. The change was based on new findings that particulates pose a greater health hazard than regulators had previously recognized, Drake said.
State DEQ issues air pollution advisory for Willamette Valley